Modified bitumen is one of the most common options for low slope commercial roofing, with “modified” referencing the addition of plastic or rubber-based polymer adhesive to the asphalt or “bitumen,” to improve performance, flexibility, UV resistance and durability. This roofing option is thought of as the next stage in asphalt built-up roofing, as it exhibits many characteristics of a built-up roof, yet allows the application process of a single-ply system. Modified bitumen is applied in layers and the number of layers determines the life span of the roof. It can either be applied with a self-adhering product or with a heat torch, but both options ensure water won’t penetrate the roof (and end up causing costly repairs).


There are two types of modified bitumen systems:

Atactic Polypropylene (also known as APP polymer) is applied using a heat-welded method, or heat torch. The consistency of the sheets result in a membrane that is more durable and flexible than a laminated built-up roof system. It’s also known to perform better in hot weather applications, and is more resistant to UV radiation.

Butadiene Styrene (also known as SBS polymer) gives the asphalt a rubber-like characteristic and is usually applied using hot asphalt, bonding adhesives, heat welding or heat activated self-adhesives. It’s known for being flexible in cold temperatures, but is more sensitive to UV radiation than APP. To prevent premature deterioration from UV radiation, SBS polymer has a granular top surface similar to the texture found on shingles. The major benefit of this product is that it has a built-up system with the quality of a factory single-ply membrane. Every flat roof is different so it’s vital the specific material you choose matches your structure. That’s why, when deciding to replace a flat roof, it’s important to work with an expert who has in-depth knowledge of all the products available. This will ensure you’re getting the best type of material for the structure you have.

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Generally, the cost of modified bitumen roofing goes down as the square footage of installation goes up. That’s why modified bitumen has been the first choice for large commercial buildings all over the world. Though, cost will vary depending on the type of material you choose and the square footage of your structure.


As with any roofing material, when replacing or repairing a modified bitumen roof it’s important to use a contractor who’s familiar with the materials and installation process. Using an expert will ensure that the repair is done correctly and there will be no future leaking or damage to the interior of your business.


The expected lifespan for most modified bitumen roofing is usually between 10-20 years, but could last up to 25 years if properly installed and maintained. Like any roof, the actual lifespan depends on the quality of the material, environment, quality of installation and maintenance. Even with the right products, it’s important to have a routine maintenance check. Over time, modified bitumen can dry out and crack, allowing water to get in and cause small leaks, which can lead to larger, more expensive problems. Having a maintenance plan in place will ensure that your building remains leak-free and in exceptional condition.


At BOLT Construction & Roofing, we know replacing a modified bitumen roof is a huge investment, especially with larger commercial properties. That’s why we not only expertly install your new roof–using only the best materials and underlayment to help protect against the Midwest’s ever-changing weather–we also develop a maintenance plan, to help your modified bitumen last its lifespan or longer. Our team of experts, along with our affordable pricing options, will get you the quality roof you need, while saving you time and money. Call BOLT Construction & Roofing today for a free consultation.